Children at a third nursery school in a city were being tested for E.coli today after an outbreak of the infection spread.
More than 80 pupils and staff at the Brooklands Nursery Primary School in east Belfast were being checked after a pupil was identified over the weekend as having a probable case of the E.coli 0157 stomach bug, which is dangerous to the very young.
It is believed the child has links with one in another east Belfast nursery who contracted the infection.
The outbreak was first identified in a pupil at the Ravenscroft Nursery School in East Belfast earlier this month.
After two further probable cases were discovered during screening, testing was extended to pupils at the Cathedral Nursery School in west Belfast who had been involved in an exchange visit with Ravenscroft.
Dr Lourda Geoghegan, from the Eastern Health and Social Services Board, said the extension of screening was a precautionary measure based on national guidelines.
"The risk to staff and children at Brooklands Nursery Unit is low," she said.
The education board is working with the Environmental Health Service, Public Health Laboratory and South Eastern Education and Library Board to get a grip on the outbreak.